Tat subunit stoichiometry in Arabidopsis thaliana challenges the proposed function of TatA as the translocation pore.
The twin arginine translocation (Tat) machinery which is capable of transporting folded proteins across lipid bilayers operates in the thylakoid membrane of plant chloroplasts as well as in the cytoplasmic membrane of bacteria. It is composed of three integral membrane proteins (TatA, TatB, and TatC) which form heteromeric complexes of high molecular weight that accomplish binding and transport of substrates carrying Tat pathway-specific signal peptides. Western analyses using affinity purified antibodies showed in both, juvenile and adult tissue from Arabidopsis thaliana, an approximately equimolar ratio of the TatB and TatC components, whereas TatA was detectable only in minor amounts. Upon Blue Native-PAGE, TatB and TatC were found in four heteromeric TatB/C complexes possessing molecular weights of approximately 310, 370, 560 and 620 kDa, respectively, while TatA was detected only in a molecular weight range below 200 kDa. The implications of these findings on the currently existing models explaining the mechanism of Tat transport are discussed.
Jakob
Mario
M
Institut für Biologie-Pflanzenphysiologie, Martin-Luther-Universität Halle-Wittenberg, Weinbergweg 10, 06120 Halle/Saale, Germany.
Kaiser
Susanne
S
Gutensohn
Michael
M
Hanner
Peter
P
Klösgen
Ralf Bernd
RB
D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D007425:Intracellular Membranes / Q000378:metabolism; D018532:Pisum sativum / Q000378:metabolism; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D021381:Protein Transport; D012995:Solubility; D013045:Species Specificity; D020524:Thylakoids / Q000378:metabolism
D029681:Arabidopsis Proteins; D021122:Protein Subunits